Non-return valves are common in industrial and domestic applications and are particularly prolific on pneumatic tyres. FIG. 1 illustrates the various components of a conventional pneumatic non-return valve 1. The valve 1 comprises an inlet casing 2 which is screw threaded within a valve stem of a tyre (not shown). The inlet casing 2 houses a shaft 3 along which a valve member 4 slidably moves. The valve member 4 is biased against a seat 5 of the casing 2 under the force of a compression spring 6 so as to close the valve 1. A spring retainer 7 is connected to an end of the shaft 3 so as to retain the compression spring 6. Pressurisation of the non-return valve 1 releases the valve member 4 from the seat 5 to allow filling of the tyre.
The conventional pneumatic non-return valve 1 suffers from at least the following problems:
i) the valve 1 has a relatively large number of components which may require periodic servicing and maintenance;
ii) the valve 1 is expensive including relatively complex machined components; and
iii) the valve is complicated in operation and thus in operation may be susceptible to failure.